The Essential Principles of Climate Change

the greenhouse effect

Throughout its history, Earth’s climate has varied, reflecting the complex interactions and dependencies of the solar, oceanic, terrestrial, atmospheric, and living components that make up planet Earth’s systems.

For at least the last million years, our world has experienced cycles of warming and cooling that take approximately 100,000 years to complete.  Over the course of each cycle, global average temperatures have fallen and then risen again by about 9°F (5°C), each time taking Earth into an ice age and then warming it again. This cycle is believed associated with regular changes in Earth’s orbit that alter the intensity of solar energy the planet receives.

Earth’s climate has also been influenced on very long timescales by changes in ocean circulation that result from plate tectonic movements. Earth’s climate has changed abruptly at times, sometimes as a result of slower natural processes such as shifts in ocean circulation, sometimes due to sudden events such as massive volcanic eruptions. Species and ecosystems have either adapted to these past climate variations or perished.

While global climate has been relatively stable over the last 10,000 years—the span of human civilization—regional variations in climate patterns have influenced human history in profound ways, playing an integral role in whether societies thrived or failed.

We now know that the opposite is also true: human activities—burning fossil fuels and deforesting large areas of land, for instance—have had a profound influence on Earth’s climate. The Intergovernmental Panel on Climate Change (IPCC) stated in 2007 that it had “very high confidence that the global average net effect of human activities since 1750 has been one of warming.”

The IPCC attributes humanity’s global warming influence primarily to the increase in three key heat-trapping gases in the atmosphere: carbon dioxide, methane, and nitrous oxide.

Extracted from Climate Literacy: The Essential Principles of Climate Sciences, published by U.S. Global Change Research Program,  2007

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